Newegg, the go-to website for any and all your technological needs, has a great promotional offer going on for Xbox LIVE–a one year subscription to the online service for just $39.99.
Even better? If you enter the promotional code, MASTERPASS, at check-out the price drops to $35.99 (below is a screenshot of my confirmation of this offer):
As a note, the code will only work if you use the MasterPass payment method, which requires you to set up an account (you can hook up your debit and credit cards to the account so no worries there). The overall price of $40 still stands, however, so feel free to take advantage of that.